1. Field of the Invention
The present invention relates generally to optical object detection systems which produce and analyze an electronic image, such as systems used to detect the presence of an occupant in a motor vehicle; and more particularly to techniques for distinguishing between different objects which have similar colors in the image.
2. Description of the Related Art
Modern motor vehicles incorporate an air bag inside the dashboard facing a passenger in the front seat. Additional air bags are being proposed for the doors to the sides of the front seat occupants. Rapid deceleration of the motor vehicle during an accident is detected and activates inflation of the air bags which then cushion the occupants. Although air bags have greatly decreased the severity of injuries from motor vehicle collisions, people are occasionally injured due to the rapid rate at which the air bag must deploy. In particular, the air bag may severely injure a small child or infant sitting in the front seat of the motor vehicle. Relatively small adults also are susceptible to injury.
As a consequence, it is now recommended that small children and infants ride in the rear seat of the motor vehicle, so as not to be exposed to the force of air bag deployment in the event of an accident. However, that does not address the situation which occurs when this recommendation is ignored and a child rides in the front seat. Furthermore, in vehicles that do not have a rear seat, such as sports cars and trucks, a child or infant must be placed in a seat that faces an air bag. In this latter situation, it has been proposed to provide an override switch to disable the air bag in front of the child. However, this approach requires that this switch be manually operated whenever a child is present and then reset to activate the air bag for adult passengers. Forgetting to appropriately set the switch for the passenger can result in dire consequences during an accident. Thus it is desirable to provide a system for automatically controlling the operation of an air bag based on the type of person in the vehicle seat.
In response to that desire, an optical system was developed that produced an electronic image of the seating area in the motor vehicle and analyzed that image to detect the presence and size of an occupant. U.S. Pat. No. 6,493,620 describes such a motor vehicle occupant detection system. These systems often use a monochromatic, solid state imager which generates a black and white image of the seating area. In order for an image to be produced at night, artificial illumination must be provided which does not interfere with the driver's ability to observe the highway. One solution illuminates the vehicle interior with near infrared (NIR) light, while an image is being acquired. Near infrared light is invisible to the human eye, yet can be detected by a solid state imager.
However, when a person dressed in black sits on a black seat, the ability of the black and white image analysis to recognize contours of that person was dramatically reduced which adversely affected determining the size of the person for airbag control. A very high percentage of clothing worn by adults and adolescences is black. Thus, the inability of the image analysis to properly distinguish the outline of a person from the black seat presents a significant limitation to the reliability of the occupant detection system.